Method of making strain-relief structure



May `1s, 1943" J. BELMONTE `METHOD -OF MAKING STRAIN-RELIEF STRUCTURE FiledJunezs,` 1940 9. Z m N .R m K m n P l allah! Patented Magi 18,` 1943 e n 'sfrnnc'rnmt:n` o n j l "Jeekpelmentererk indiani.. estimer te ont.

Flexible Shaft Company,l Chi "corporationoflllinoin i 1 Application Innere, mit, seieinetiam icieini. (ctie-49) o f :This invention relates to thewmanuiacture oi articles having flexible portions Vadapted for con- "particularly, `my

are gripped tightly operation thereof.

,f nection to solid structuresvand wherein pulling .tensions are imposed` on the connection. lMore invention relates to strain-relief 4structures or the like for electric cords used for attachmentto electric appliances suchas toasters,

ilatirons.` wallie makers,Y coiIee makers, etcl. My

i invention also relates tothe` inethodoi` manufacturing 'a structure cir-Particle ofthis kind.

1 One of the sources; of serious diiilculty in appliance plugs is the connection between the cord fvterminals and the plug. Because of the nature i oi the devices-with which the plugs are used. and `*the fact. that these devices are usually hot,` the AVplug lis commonlyV removed from `the 'appliance 1 by pulling'on the cord. vWith a` well made and emcient plug the terminal posts of the appliance thisfin `adciltionrto the Agrowth of electrolytic'cor- `rosion products between-the clips and posts accompanying high tempera-tures` and `:prolonged operation, tend dimcult and placca. severe straino'n the terminal connections a result, the` cord is apt to be pulledioosefrom theplug' if adequate strain relief is not provided. `This is recognized by manufacturers aswell y Fire Underwriters,` the latter ot which require Vas by thewNational Boardof of, 3. inch-pounds yapplied which in some instanceswill interfere withvthe Animportantobject of the invention is,` there..

lore, to provide an improvedjstrainfreliei! 'strucw turefor electric cords whichmay be applied both tothe detachable type of attachment'plug and `to cordswhich are intended-to )qe-permanently l` `attached toanappliance. i

i More particularly, myiinvention `for one of its objects .the provision of a strain-'relieistruc- `ture characterized by o a` homogeneous and permato make thewremoval of the plug union and the structure .tachable for permanent type. `'llliis homogeneous in which it 1S embodied i 3 Zivesnew and improved results,as will be pointed out more fully hereinafter.

. Another. object of my invention istoA provide a novel method 'ofV Y Vstructures of the character Y ized by the steps of treatinga vmanufa'fcturing' strain-'relief described characterbrous. sheath i' the electric cord with a heat reactive me1deb1e resin se es te thoroughly impregnate the structure and to provide a portion A"capable of being molded,fand` subjecting said by the plug terminal clipsl and Y i treated portionfto.; l `which is shaped to provide the coniiguration of the intended strain-relief` body, which the said treated portion heat and pressure in a `mold in consequenceof I is Vmolded into a homogeneous structure of the desired Shania` In the preferred embodiment as applied to a strainrelief `forfcoaction with an attachmentplg the steps are carried out substantiallyas follows: e First, the fibres or strands of the nbrous or woven 1. sheath are loosened and separated so topro- `vide an enlarged, spread-out portion. This portion is then treated with a heat reactiire mold- `ableyresin such as phenol-formaldehyde`resin or .ureayfornialdehyde resin, so trea d issubjected to heat and pressure in aV mold asI bove described with the result thatthe resinous` material becomes intimately associated with thei bres 0f the insulation and illls the "Small intersticjes` between thefbres and strands with the resiiltrthat a solid homogeneous structure is .i obtained which has strength, durability,` low mois..

ture absorption,` and lg unaffected by heat to i Vwhich these connections are ordinarily subjected. i The solid structure provides exceptionally dura- "ble thrust resisting surfaces; and the' s'olid pontion is sounited Va novelmethod e A cle of the character described`may be commerwith Vthe ilexible cord'as not to pair the connection between the Vtwo but rather tolprovidea strong and durable connection.

L Another object of my in of manufacture whereby an' arti 'cially produced at comparatively4 low cost.`

Another object is toprovide a novellmethod of manufacture distinguished from prior molding Qmethods, in that an assembled fibrous structure .capable of absorbing or retaining a moldable syn Y. thetic resin or cellulose derivative is treated in nent union `ofthe nbreus sheath er the eieetrie 'o plug orI the appliance, acthe connection ,is of thedecord with tnelseiid` bodywhicn prevldesfgthe )strain-relief surface and which coacts,directly Y with `the attachment `V@eenling to whether partwith said resin and aparticular section of the assembled fibrous structure ismolded to a solid section while the remaining portion retains itsriiexible physical identity. C f Othen objects e and attendantv advantages will be appreciated by those skilled in'this `art as portion of'the o and then the portion vention is to provide Figs. 4 and 5 are somewhat diagrammatic` views of the cord on an enlargedscale ,showing the different steps in the process of manufacture which will be described more fully hereinafter;

Fig, 6 is a perspective View on the corresponding scale showing a iinished article in this ernbodiment of my invention;

Fig. 7 is a further enlarged view showing a longitudinal seetionthroughrthe finished article,

Fig. 6;

Fig. 8 isa sectiontaken on the section line 8-8 of Fig. 7; and

A 9 isa corresponding section showing a modification inthe manufacture.

` l In the drawing 4I have shown my invention as applied to' astrain-relief structure for an appliance attachment plug. The plug itself may be of any suitable or preferred construction-but adapted to have one or more strain-resisting j shoulders Il adapted for coaction with compley lmenta'ry Ysurfaces of the strain-relief structure whichis here designated generally byV I2. In

this instance the plug. body is-formed of two 2 half-sections I3 aridA I4 shaped interiorly Vto pro- 't vide grooves l5vfor the reception of contact'elements l5, and an openingl'lfor reception of the terminal end of the electric cord and its t' strain-relief structure.

vbe fastened together by suitable means well u A known in this art.

The plug sections may Y In a plug of this type it is desired to protectY the .electric cord at its'entrance into the plug body by means of Ya spring ,wire sheath 18,. the inner end of which is re-l tained ina groove I9 formed'in the plug sections.

Referring vnow more particularly to the manufacture of the strain-relief structure as applied to attachment plug of the kind described, it will be observedv that the first step is to strip or re- `move the fibrous cover or sheath from the end o' of the cord which is to be attached to the plug,

leaving thetwo terminals of the conductor wires bare. In the type of 'electric cord shown in the drawing each conductor may be individually c overed by a rubber insulation 2l and these insulated wiresv are encased in a sheath 22 of fibrous insulation material such as asbestos, and

the latter isk encased in a woven fabric sheath 23. The asbestos fibre 22 and the fabric sheath 23 are stripped back and loosened at the end of Vthe cord jsufilciently to provide an enlarged spread-out portion inwhich the fibres and rstrands are separated and make a considerable mass` designated generally'by 24. The ends 25 of the conductor wire are then turned back upon themselves substantially as shown in Fig. 4, preparatory to the treating step whichv follows. In this step the spread-out end of the cord is treated'with a heat reactive moldable resin in such manner that the resinous material becomes intimately associated with the fibres and strands and fills the interstices thereof. Preferably, this end of the cord is emersed in a resin varnishy sufficient to permit the absorption of an adequate amount of resin from the solution. After a short drying period of approximately 10 minutes, the

resin impregnated cord is placed within a mold (not shown) of the type commonly used for molding phenolic resin products and in this instance shapedto provide the configuration of the strain-relief body heretofore designated as I2. Following this there is placed within the mold and in juxtaposition to the treated portion of the cord, a piece of resin impregnated paper designated 26 of a shape and section bearing a definite relation to the treated portion of the cord and the resultant molded shape. In actual practice I prefer to use what is known as Rogersboard, which has a fibre paper base treated with a heat reactive resin. As a substitute for Rogersboard any fibrous material capable of absorbing heat reactive resin may be used. Material of this kind is available in sheet form and lends itself particularly well to stamping the piece to any desired shape. In the present instance the piece is stamped to T-shape conforming Awith the shape of the mold cavity. It is also noted that the piece 26 has a central portion 2l extending lengthwise of the cord body beyond the loosened portion thereof and laterally extending portions 28 following what is intended to be the resultant shape of the strain-relief body. Added significance is attached to the thickness of this piece of resinimpregnated paper because this is a factor in the final thickness of the molded section which is intended to have a predetermined dimension. It will be apparent that the final molded section will be a composite of the resin impregnated paper `and the resin impregnated cord. As shown-in Fig, 5, the wire terminals 25 have been bent at 29 in the opposite direction from that shown in Fig. 4 so that they lie in offset parallel relation with the main body of the cord. These terminal ends are confined in the mold in definite relation to the ultimate molded section so that they will project from this section in the desired relation thereto.

l With the materials arranged in the mold as def scribed, the next step is to close the mold usually by lowering the plunger into the cavity of the mold and develop the required heat and molding pressure upon the resin impregnated paper'and the resin treated end of the cord. This pressure, in combination with the heat that is present in the mold, will cause the resin in the Rogersboard and the resin in the fibrous material at the end of the cord to fuse together in a solid homogeneous structure. I have found that molding temperature in the neighborhood of 350 F.

and molding pressure of fromv 3000 to 4000 pounds per square inch is adequate for a molding operation within the space of approximately 60 seconds. After the molding operation the molded article' is ejected from the mold and any excess flash which may be kept quite small by the mold design is removed from around the wires 25. It is.-ol course, understood that in commercial production using this method, multiple cavity molds may be used, thus reducing the unit time and `estratta? .L 3

cost formoldin'g each piece. As a result of the treating of the fibrous material with a synthetic. v `resin and then molding the treated portion to a e predetermined shape the resinous material is fused into the most intimate andpenetrating relation to the fibres: and fills all of the interstices therebetween, thereby producing a solid, coherent and homogeneous bodystructure reinforced and bonded by the fibrous material. 'Ihis makes a strong and durable body structure of the dev sired shape characteristics joined to` a flexible fibrous structure. 'Ihis may be accomplished with or without the addition of a resin impreg- 4 nated piece such as a Rogersboardsection. However, in-the embodiment shown in Fig. 9,`paper pieces 3| conforming to the shape of the piece? 26 but of thinner cross section are applied to opposite sides of the loosened and spread-out terminal portion of the fibrous cord. Here also the body of this treated portion combined with the impregnated paper constitutes the desired cross section of the `solid strain-resisting body. It Will be observed that in the attachment plug embodiment the tension forces resulting from pull on the iiexible cord are distributed to the strain-resisting molded section through the many fibres and strands whose iiexibility characteristics gradually merge into the homogeneous structure of such section. The molded section is` at the same time reinforced and .tied together by the fibres and strands. VIt follows that the Y tension forces exerted bypulling and twisting of the cord are `not transmitted to the terminal wires but rather they are resisted by the reaction of the solid body I2 against Ythe abutment faces ll and the adjacentside wall faces on the plug body according to the direction of l the forces. This function is further attained by reason of bending the conductor wires 2| in diverging relation, as shown in Fig, '7, and in confining these wires in the solid molded bodywhichv takes vall of the pulling and twisting strains from the `connections between the wire terminals' 25 and their contact elements |6.

From the foregoing it will be apparent that I have provided a new method ,of making articles of manufacture in which a flexible portion of fibrous material is `joined to and becomes a part of a homogeneous molded section. As applied to an appliance cord, the cord proper outside the Vplug receptacle or casing is flexible and the strain-relief portion locatedl incoaction with the' casing is the molded section. This molded' section is an assembled fibre structure having excellent wear and strainfresisting properties and providing a durable union with the flexible cord. The molded section also has the further desirable teriorate from heat. An appliancel cord is constructed herein will withstand pulling tensions and twisting or torsion loads far in excess of the Underwriters requirements above mentioned. i A y Where my invention-is applied to an Velectric cord intended to be permanently attached to an appliance as distinguished from connection to an attachment plug which has'detachable connecl tion with the appliance, lan intermediate portion` of ,the cord will be treatedin aV resin solution,` although it is not essential that the fabric sheath be loosened for separating the fibres or` strands.

Upon this treated portion will be molded a section shaped for coaction with the appliance wall or other structure. For example, where the cord passes througha Wall of the appliance and it is desired to fasten the cord thereto in a strainrelief connection, the molded section would` be annular, circumscribing the cord, and thesection would have an annular groove which receives the appliance wall and provides the strainrelief surfaces.- With this construction the, pulling forces on the cord are resisted by the wall structure and are not transmitted to the terminal connectionsof the cord.

My invention also contemplates broadly an assembled fiber structure capable of absorbing and retaining a moldable synthetic -resin or cellulose derivative and the treating of this structure in part with said resin so that a given portion of the fibrous or wovenstructure is capable of being reduced to a solid molded section while the remainder retains its soft or fiexible physical identity. This may be accomplished either with or Without the addition of a resin impregnated piece or section shaped to conform with the general configuration of the resultant molded section. In this broader phase of my invention the assembled fibre structure may be in the `form of assembled fibres or strands as in the case of woven fiat material as distinguished from an assembled structure such as an electric. cord.

`physical properties of low moisture absorption, electrical insulation, and it does not soften or de- In such case the molded section may be of any desired shape, pattern or coniiguration. v For example, the assembled fibrous material may be an annular sheet and the molded section may be applied to the peripheral edge portion, mak-` ing a structure suitable for diaphragms, valves. filters, partitions, and the like.

` While I have described several embodiments of my invention, it will be understood that I `do. not wish to be limited thereto since many modifications may be made,`and I therefore contemplate bythe appended claim to cover any such modiiications-a fall within the true spirit,

and scope ofmy invention.

I claim:

The method of making a strain-relief structure for a fibrous` sheath electric cord comprising the steps of stripping the flbrouscover from` Y mate external shape of the strain-relief structure, with the terminals extending from the mold cavity at the opposite strain-relief portions, subjecting the material in the mold to heat and pressure sufficient to fuse the resin materials intoV a homogeneous mass in which said materials are fused into intimate relation Vto the fibers and` strands, and allowing said material to cool to a solid body in which the sheath cord is molded and in which the spread-out portion is incorporated in the oppositely extending strain-relief portions. Y

JACK BELMONTE. 

